In preparation for adding more synchronization primitives, move the
Semaphore implementation into its own module.  There is enough stuff
associated with each primitive that it can be confusing if they are not
in their own modules.

Signed-off-by: David Brown <[email protected]>

Add support for declaring static instances and arrays of the sys Mutex
and sys Condvar.

Signed-off-by: David Brown <[email protected]>

Although it is tradition in Rust to have types such as Semaphores and
Mutexes not implement Sync, these primitives, built as thing wrappers
become fairly useless.  Sharing them would require `Arc`, which requires
alloc. Presumably someone wanting to use lower level primitives would
also not likely be wanting to use allocation.

For the most part, these primtives have as their real purpose to be used
in the implementation of the higher level synchronization primtives,
such as sync::Mutex.

unlock is unsafe because it is required to only call unlock on the same
thread that locked.

Signed-off-by: David Brown <[email protected]>

Add a version of the philosopher's demo that is built around sys::Mutex,
in it's simplest use case.

Signed-off-by: David Brown <[email protected]>

Create higher-level Mutex and Condvar types that are similar to
std::sync::Mutex and std::sync::Condvar.

The main difference is that the only current constructor for this
requires the sys Mutex and sys Condvar from the sys versions that are
statically allocated.

Signed-off-by: David Brown <[email protected]>

Build a syncer that coordinates the forks using a single Mutex/Condvar
pair, where the Mutex protects the data, and Condvar is used to
coordinate.  This is a common paradigm for shared synchronization.

Signed-off-by: David Brown <[email protected]>

A simple wrapper around Zephyr's k_queue.

Signed-off-by: David Brown <[email protected]>

Create an implementation of bounded channels, in the spirit of
crossbeam-channel.  Currently, only the bounded channels are supported,
an as we don't yet support recovery from panic, ther is no poisoning.

As the underlying Zephyr queues don't support deallocation, drop is also
a no-op.

Signed-off-by: David Brown <[email protected]>

Add a synchronizer for forks based on sending messages over channels to
a worker thread.

Signed-off-by: David Brown <[email protected]>

Rather than just printing a bunch of information out as the various
philosopher threads dine, use some data protected within a Mutex to
collect statistics, and print those out periodically.

Signed-off-by: David Brown <[email protected]>

Although this function has constraints on how it can be used (the thread
that calls unlock must also have called lock).  However, according to
the documentation, it detects this, and returns an error.  As such, the
wrapper in Rust does not need to be `unsafe` but can merely reflect that
error code in the `Result` that it returns.

Signed-off-by: David Brown <[email protected]>

Now that `sys::Mutex::unlock` has lost its `unsafe`, we don't need an
unsafe block for it.

Signed-off-by: David Brown <[email protected]>

This function returns initialized memory, and is therefore inherently
unsafe.  Added some commentary about how it is used safely.

Signed-off-by: David Brown <[email protected]>

Move the Wrapped trait above the StaticKernelObject so that the traits
are immediately declared after the type the apply to.

Signed-off-by: David Brown <[email protected]>

Although these, in their current state, are safe to Clone, having these
semantics will make it difficult for us to later add these types that
are allocated from a pool.

Uses that currently expect to clone can generally wrap these in an Arc,
to allow for the sharing.

Signed-off-by: David Brown <[email protected]>

The `Fixed` type encapsulates something that can either be a statically
allocated object or a dynamically allocated one.  It is conditional on
`CONFIG_RUST_ALLOC`, and if that is not defined, will just end up
represented as the underlying static pointer.

Add support for dynamically allocated Semaphores.  These can be freely
allocated, but are not usable from userspace.

Add a sample that implements the forks using dynamically allocate
semaphores.

Signed-off-by: David Brown <[email protected]>